Fifteen Theme: Finding CSS code (4 posts)

Hi,
I'm pretty new to WordPress and am currently finding my way around customising my Fifteen Theme. I have inspected my site via Firebug, and located CSS lines where I can change the main content background colour from the default grey to white...but when I go to my dashboard>appearance>editer, and try to locate that CSS line in the stylesheet I cant find it...in fact the CSS that comes up on Firebug doesnt appear to be the same generally. Any ideas on what might be wrong or what I need to do? thanks very much!!!

OK great, will do. I've had a look at different sites providing instructions on how to set up a child theme...and they all mention creating a new theme folder to begin with...but they don't make it clear where to create this new folder...Can you help?
thanks!